The invention relates to a fiber structure electrode plaque for increased-capacity voltage accumulators, comprising a needle felt web made of synthetic fibers which, after activation, is chemically metallized, and is reinforced by metal plating.
Today, as in the past, there is a constantly increasing demand for a mobile decentralized power supply. In this context, accumulators (batteries and other accumulators) are the leading suppliers of an electric energy that is not bound to any location and is available for a limited time. The most wide-spread accumulators are probably those that are equipped with an aqueous electrolyte; for example, with an acidic electrolyte, as in lead accumulators; or with an alkaline electrolyte, as in nickel cadmium cells, nickel hydrogen cells, nickel iron cells or nickel zinc cells. Accumulators which are equipped with an organic electrolyte, a melting electrolyte or a solid electrolyte are also gaining in importance.
The efficiency of an accumulator depends essentially on two factors, specifically the loading capacity of the electrodes and the maintaining of the capacity of the accumulator. In addition, other aspects are becoming increasingly important today, such as the prices of the requisite metal on the world market, or questions concerning the recycling of the used-up accumulators.
In practice, a compromise must frequently be made relative to a particular usage, between the loading capacity of the electrodes and the maintaining of the capacity of the accumulator; i.e., the construction of the electrodes must be adapted to the intended function. Applied to individual battery systems, this means that, for example, for accumulators with lead/lead dioxide electrodes or for accumulators with nickel cadmium electrodes, very specific types of electrodes were developed for the respective usage of the storage cell. Types of electrodes that should be mentioned are: large-surface plates, grid plates, tubular plates, ironclad plates or also self-baking electrodes.
Recently, attempts have been made to use, independently of the particular battery system, a uniform carrier plaque for the electrodes. For this purpose suitable porous synthetic materials have been used, such as foamed materials, nonwoven fabrics or needle felts for the carrier plaque. In the manufacture of the carrier plaque, the synthetic substrate is first activated by means of noble-metal-containing compounds, for example, on a palladium tin base. The thus pretreated surface of the synthetic substrate is then chemically metallized, and the formed metal layer may be reinforced by plating with another metal layer. In this manner, electrode plaques are obtained that have a uniform structure, in particular a porous synthetic substrate which is coated with an appropriately selected metal layer. In this case, the correspondingly selected thickness of the synthetic substrate determines the volume-related capacity of the later existing electrode. The selection of the metal layers deposited on the synthetic surface is determined by the intended use in a specific battery system. The thickness of the metal coating applied to the synthetic surface ultimately determines the capability of the electrode plaque to ensure, during use of the accumulator, current transport from the electrode plaque to the active mass with a higher or lower electric resistance.
The manufacturing of carrier plaques of this type for fiber structure electrodes today is part of the state of the art, such as is disclosed, for example, in the German Patent Documents 33 18 629; 36 37 130; 36 31 055 and 37 10 895. In order to assure efficient functioning of the electrodes in such devices, it is necessary that a sufficiently high porosity be maintained in the electrode plaques. When this requirement is observed, however, in the case of needle felts, the nominal thickness can be reduced only to approximately 1.5 mm, thus resulting in a reduction of the electric capacity of the electrodes which are so equipped. Although high-capacity constructions for electrodes that are offered as alternatives, such as self-baking electrodes, have clear advantages with respect to their loading capacity, they are much more expensive to manufacture.
It is therefore an object of the present invention to provide an electrode plaque made of synthetic fibers, in which the low-cost availability of the highly porous carrier material, and its easy processing into electrode plaques are utilized.
Another object of the invention is to provide such an electrode plaque which achieves increased electric loading capacity of an accumulator equipped therewith.
These and other objects are achieved according to the invention by means of a fiber structure electrode plaque fabricated from needle felt web having characteristic numbers according to the invention as indicated below, and in which the needle felt web is needled from both sides over its whole surface and has a nominal thickness of only 0.5 to 1.0 mm. In such electrode plaques the strong forces of expansion which occur during the cycle operation of the electrode due to the volume work of the active mass can still be absorbed because of the increased mechanical stability of the electrode plaque caused by the double needling of the needle felt. Improved electric loading capacity is therefore obtained for the fiber structure electrode plaque according to the invention, which has a smaller thickness than the plaques according to the known state of the art. The reason is that the stability of the electrode plaque does not suffer any premature damage due to the charging and discharging operation of the cell.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.